Wave Spreading and Wave Drift Loads for a Standard LNG Carrier in Shallow Water

2010 ◽  
Author(s):  
Emmanuel Sergent ◽  
Mamoun Naciri
Keyword(s):  
Natural Gas ◽  
Shallow Water ◽  
Natural Frequency ◽  
Water Depth ◽  
Storage Capacity ◽  
Mooring System ◽  
Spectral Densities ◽  
Floating Structures ◽  
Wave Drift ◽  
The Impact

The need for LNG export and import terminals is anticipated to grow as natural gas progressively accounts for a larger fraction of worldwide consumed energy. These terminals are preferably located nearshore i.e. in relatively shallow water. Design of floating structures is most of the time performed assuming long-crested waves. In shallow water, diffraction of waves by a variable bathymetry can result in wave spreading i.e. in short crested seas. The effect of short crested seas on the wave drift load spectral densities for a 135,000m3 storage capacity LNG Carrier in 15m water depth is investigated. It is shown that the impact of wave spreading on drift loads depends on the natural frequency of the moored vessel and thus on the stiffness of the mooring system under consideration. Although response calculations are not performed herein for reasons to be discussed, it is conceivable that wave spreading could adversely affect loading/offloading terminal availability for stiff moorings.

Numerical Study of Phase Change Influence on Wave Impact Loads in LNG Tanks on Floating Structures

2018 ◽  
Author(s):  
Matthieu Ancellin ◽  
Laurent Brosset ◽  
Jean-Michel Ghidaglia
Keyword(s):  
Natural Gas ◽  
Phase Change ◽  
Numerical Study ◽  
Model Tests ◽  
Impact Loads ◽  
Wave Impact ◽  
Floating Structures ◽  
Physical Phenomena ◽  
The Impact ◽  
Phase Phase

Understanding the physics of sloshing wave impacts is necessary for the improvement of sloshing assessment methodology based on sloshing model tests, for LNG membrane tanks on floating structures. The phase change between natural gas and liquefied natural gas is one of the physical phenomena involved during a LNG wave impact but is not taken into account during sloshing model tests. In this paper, some recent numerical and analytical works on the influence of phase change are summarized and discussed. For the impact of an ideally shaped wave, phase change influences two different steps of the impact in different ways: during the gas escape phase, phase change leads to a higher impact velocity; for entrapped gas pockets, phase change causes a reduction of the pressure in the gas pocket. However, this influence is quantitatively small. The generalization to more realistic wave shapes (including e.g. liquid aeration) should be the focus of future works.

Impact of Elastic Body on the Deep and Shallow Water

2013 ◽  
Author(s):  
Alexander A. Korobkin ◽  
Tatyana I. Khabakhpasheva
Keyword(s):  
Shallow Water ◽  
Elastic Body ◽  
Water Depth ◽  
The Body ◽  
Complex Structures ◽  
Water Impact ◽  
One Dimensional ◽  
Mode Method ◽  
Bending Stresses ◽  
The Impact

Two-dimensional unsteady problem of elastic body impact on liquid free surface is considered. The water is either of infinite depth or shallow. We are concerned with the effect of the water depth on the bending stresses in the structure caused by the fluid-structure interaction. The Wagner model is used for infinite water depth. In the case of shallow water impact, the hydrodynamic problem is one-dimensional but nonlinear. Both problems for deep and shallow waters are solved numerically by the normal mode method. Two shapes of the body, cylindrical shell and elastic wedge, are considered. The impact conditions and the structural characteristic are identical. The bending stresses in the structure are investigated. It is shown that the bending stresses for impact on shallow water are greater than those for the infinite water depth. The developed methods and approaches can be combined with FFM to include complex structures.

Coupled Analysis of Floating Structures With a New Mooring System

2011 ◽  
Author(s):  
Zhiming Yuan ◽  
Chunyan Ji ◽  
Minglu Chen ◽  
Yun Zhang
Keyword(s):  
Water Depth ◽  
Deep Water ◽  
Coupled Analysis ◽  
Mooring System ◽  
Full Time ◽  
Analysis Method ◽  
Floating Structures ◽  
Motion Performance ◽  
Improved Performance ◽  
Hydrocarbon Reserves

As the exploitation of hydrocarbon reserves moves towards deeper waters, the floating structures are becoming more and more popular, and the catenary and taut mooring systems are two widespread mooring systems which are used for these floating structures. However, both of them have their inherent drawbacks. The aim of the present work is to develop and validate a new mooring system which will overcome these shortcomings. To this end, the motion performance of a semi-submersible platform is simulated by employing a full time domain coupled analysis method. It is shown that the new mooring system yields very good motion performance when benchmarked against the taut mooring system, and the reasons for this improved performance are discussed. Also, the new mooring system is compatible with the characteristic of catenary mooring system, which eliminates the requirement of anti-uplift capacity of the anchors. The second aim of this paper is to explore the proper water depth in employing this new mooring system. For this purpose, several typical water depths are simulated. It is found that the new mooring system works well both in deep water and ultra-deep water. But, as the water depth becomes deeper, the advantages of the new mooring system are reduced.

Dropped Polyester Mooring Line Qualification for Reuse

2021 ◽  
Author(s):  
Craig R Gage ◽  
Pierre F Liagre ◽  
Caspar N Heyl ◽  
Cesar Del Vecchio
Keyword(s):  
Gulf Of Mexico ◽  
Water Depth ◽  
Cost Savings ◽  
Mooring Line ◽  
Mooring System ◽  
Potential Cost ◽  
Mooring Lines ◽  
Minimal Damage ◽  
Recovery Effort ◽  
The Impact

The Perdido platform is a spar located in a water depth of 7,825 feet in the Alaminos Canyon Block 857in the Gulf of Mexico. The mooring system consists of nine mooring lines in three groups of three, spacedapproximately 120 degrees apart between each group. Each mooring line is composed of a platform chain,a multi-segment polyester rope including a 120 feet long test insert at the top, a ground chain, a pile chainand other associated connectors. The mooring lines are connected to suction piles. The Minimum BreakStrength for the Perdido polyester mooring line is 4,000 kips. Installation of the spar hull was completed inSeptember 2008 and the topsides was set in March 2009. The spar and its mooring system were originallydesigned for a twenty (20) year life. On May 4, 2019, mooring line # 6 (ML6) was contacted by a marine vessel down line and was severed.Contact occurred along the polyester test insert. A recovery effort was planned, and the mooring line wasreplaced in early June. The original ML6 was recovered from the seafloor on June 4, 2019 as a part of thatcampaign and submitted to an initial inspection. This paper is not intended to go into either the cause of the incident or the replacement of ML6 but willlook to the inspection of the recovered mooring line and explore its suitability for reuse. Initial inspection ofthe lines suggested minimal damage to the polyester rope segments and raised questions to the impacts of 10years of use. Testing was envisioned as a learning opportunity for the impact of service on polyester mooringand was reinforced by the potential cost savings that could be attained though reuse. A methodology wasdeveloped, supported by initial inspections and a suite of testing was performed. The results of these testsare presented in the following, along with a proposed process for assessing and considering reuse of a linefollowing a drop. Additionally, conclusions will be shared for the process, the results, and the potentialramifications for the industry.

Analysis on Motions and Green Water of FPSOs in Shallow Water With Non-Collinear Environments

2010 ◽  
Author(s):  
Bin Guo ◽  
Long Fei Xiao ◽  
Jian Min Yang
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Wind Waves ◽  
Single Point ◽  
Green Water ◽  
Floating Structure ◽  
Floating Structures ◽  
Head Waves ◽  
Run Up ◽  
Yaw Angle

The paper presents motions and green water of a FPSO in shallow water with different wave headings. In non-collinear directions of wind, waves and current, the FPSO does not always encounter head waves, which probably induces specialties in motions and green water especially because of the complexity of shallow water hydrodynamics. Time-domain numerical simulation and model test are carried out in order to analyze motions of a single-point moored FPSO. Green water and wave run-up along the side of a fixed FPSO are simulated in a 3-D numerical wave tank, and results are compared with that of model tests. It is shown that the influence of the yaw angle on motions of a FPSO is considerable and green water occurs more frequently around the mid-ship when the FPSO encounters a big wave heading. In the same water depth, roll and pitch motions of the FPSO under higher wave are lower instead but green water occurs; in the same wave situation, the motions of the FPSO in a lower water depth are lower, but green water occurs more severely. In general, water depth has an important influence on green water of FPSOs in shallow water. The hydrodynamic character of large floating structures in shallow water, especially the green water, should be taken into account carefully for determining the design load and freeboard of a large floating structure.

scholarly journals Analysis and simulation of a single buoy mooring system based on sea environment

2014 ◽  
Vol 17 (3) ◽  
pp. 146-155
Author(s):  
Quang Xuan Le ◽  
Hien Vo ◽  
Huy Huu Nguyen ◽  
Nhat Ly Minh Tran ◽  
Thang Toan Nguyen ◽  
...  
Keyword(s):  
Water Depth ◽  
Coastal Waters ◽  
Single Point ◽  
Maximum Load ◽  
Mooring System ◽  
Optimal Length ◽  
Floating Structures ◽  
Guidelines And Standards ◽  
Mooring Chain

Single Point Mooring (SPM) is of great use to offshore floating structures which are currently in use in Vietnam’s coastal waters. However, this country is facing the lack of the related guidelines and standards for analysis, simulation and design of SPM system. This fact is the rationale for this paper which is aimed to propose a procedure for computation of the effects of sea environment on a SPM system. Specifically, the procedure enables the identification of maximum load exerting on the mooring buoy. Then, such identification together with the water depth parameter enables the determination of the optimal length and diameter of the desired chain. Finally, this paper presents a primary simulation of the mooring chain system according to various water depth conditions.

Diffraction/Radiation of 135,000M3 Storage Capacity LNG Carrier in Shallow Water: A Benchmark Study

2009 ◽  
Author(s):  
Mamoun Naciri ◽  
Emmanuel Sergent
Keyword(s):  
Shallow Water ◽  
Load Transfer ◽  
Storage Capacity ◽  
Transfer Functions ◽  
Second Order ◽  
Diffraction Radiation ◽  
Hull Form ◽  
Benchmark Study ◽  
Wave Drift ◽  
Key Issues

The HAWAI (sHAllow WAter Initiative) JIP was launched in 2005. The objective was to improve the reliability of Offshore (LNG) Terminals by combining the expertise of offshore hydrodynamics and coastal engineering to better address key issues regarding motion and mooring prediction methods in shallow water. One of the key issues identified was the diffraction/radiation calculation as this is the main foundation of all motion and mooring analyses. Comparisons of second order wave drift load transfer functions predicted by leading diffraction/radiation software for a typical 135,000m3 storage capacity LNG Carrier (LNGC) had shown notable differences (see Ref [1]). A benchmark study was launched for a standard LNGC in 15m water depth. Seven leading commercial diffraction/radiation software were used for this comparison (AQWA, DELFRAC, DIFFRAC, DIODORE, HYDROSTAR, WADAM and WAMIT). Comparison was first done by specifying the hull form in CAD format and then by specifying the mesh. First and second order results are presented and conclusions are drawn regarding the robustness of these codes.

A New Interpolation Method for FPSO Motion and Wave Drift Load Transfer Functions

2011 ◽  
Author(s):  
Ste´phanie Stafrach ◽  
Mamoun Naciri
Keyword(s):  
Spectral Density ◽  
Shallow Water ◽  
Load Transfer ◽  
Storage Capacity ◽  
Transfer Functions ◽  
Interpolation Method ◽  
New Method ◽  
Wave Drift ◽  
Floating System ◽  
Response Amplitude Operators

A new method of direction-wise interpolation is proposed. Its merits are first presented by considering the interpolation of 1st order motion Response Amplitude Operators (RAOs) and 3D (ω1, ω2, θ) wave drift load Quadratic Transfer Functions (QTFs). In a recent publication (see Ref. [1]), the importance of wave spreading on the spectral density of wave drift loads for a standard storage capacity LNG Carrier (135,000m3) in shallow water has been demonstrated. The computation of above-mentioned spectral densities requires the precalculation of a large number of 4D (ω1, ω2, θ1, θ2) wave drift load QTF and interpolations between the calculated directions. Application of the new method is investigated in this more challenging context. Examples are selected in the buoyant LNG floating system area with an LNG Carrier in shallow water and an FLNG in deep water.

scholarly journals Influence of Erodible Beds on Shallow Water Hydrodynamics during Flood Events

Water ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 3340
Author(s):  
David Santillán ◽  
Luis Cueto-Felgueroso ◽  
Alvaro Sordo-Ward ◽  
Luis Garrote
Keyword(s):  
Numerical Simulations ◽  
Shallow Water ◽  
Water Flow ◽  
Water Depth ◽  
Velocity Fields ◽  
Economic Losses ◽  
Flood Events ◽  
Erosion And Deposition ◽  
The Impact ◽  
Erodible Beds

Flooding has become the most common environmental hazard, causing casualties and severe economic losses. Mathematical models are a useful tool for flood control, and current computational resources let us simulate flood events with two-dimensional (2D) approaches. An open question is whether bed erosion must be accounted for when it comes to simulating flood events. In this paper we answer this question through numerical simulations using the 2D depth-averaged shallow-water equations. We analyze the effect of mobile beds on the flow patterns during flood events. We focus on channel confluences where water flow and sediment mobilization have a marked 2D behavior. We validate our numerical simulations with laboratory experiments of erodible beds with satisfactory results. Moreover, our sensitivity analysis indicates that the bed roughness model has a great influence on the simulated erosion and deposition patterns. We simulate the sediment transport and its influence on the water flow in a real river confluence during flood events. Our simulations show that the erosion and deposition processes play an important role on the water depth and flow velocity patterns. Accounting for the mobile bed leads to smoother water depth and velocity fields, as abrupt fields for the non-erodible model emerge from the irregular bed topography. Our study highlights the importance of accounting for erosion in the simulation of flood events, and the impact on the water depth and velocity fields.

Mooring System Design Approach: A Case Study for MARMOK-A Floating OWC Wave Energy Converter

2018 ◽  
Author(s):  
Imanol Touzon ◽  
Borja de Miguel ◽  
Vincenzo Nava ◽  
Victor Petuya ◽  
Iñigo Mendikoa ◽  
...  
Keyword(s):  
Water Depth ◽  
Characteristic Line ◽  
Axial Stiffness ◽  
Mooring System ◽  
System Configuration ◽  
Static Properties ◽  
Technical Requirements ◽  
Line Mass ◽  
Total Plant ◽  
The Impact

This paper presents a methodology and a flowchart of steps to take for a, consistent and rapidly convergent design of catenary mooring systems. It is subsequently applied for a floating Oscillating Water Column WEC MARMOK-A developed by Oceantec Energías Marinas, in order to fulfill the technical requirements of such dynamic systems. The approach, based on the catenary equations, considers the water depth as a design scale factor for the mooring system, leading to an equivalent static mooring performance. In general, a mooring system configuration is described by the number and distribution of lines; thus, as a preprocess in the herein described procedure, a database is built for different line lengths. The main advantage of the procedure is that once that, after characterizing a mooring system configuration at a specific water depth with a specific line mass and axial stiffness, the database built can be used for any other water depth with any line mass and axial stiffness, accelerating the design optimization process. Mooring static properties are derived for a given material elastic modulus, lines’ mass and water depth. The mean offset and horizontal stiffness are afterwards derived with lines pretension and steady environmental forces (mean wave drift, current and wind) as well as maximum offset and characteristic line tensions. Finally, the process is applied for different lines pretensions to achieve an objective horizontal stiffness of the structure. The introduced procedure is presented through its application to the MARMOK-A device at a 90m depth site moored by means of a Karratu named mooring configuration. Results are presented in terms of total lines mass, device maximum expected excursion and required footprint for different horizontal stiffness and lines mass in order to give an insight of the impact on total plant cost indicators.

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